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Abstract:

A method for producing a silicone resin sheet includes the steps of
forming a first coating layer by applying a first silicone resin
composition which contains a first organopolysiloxane and a second
organopolysiloxane; forming a precursor layer from the first coating
layer by reacting the first organopolysiloxane with the second
organopolysiloxane so as to have a conversion ratio of 5 to 40%; and
forming a second layer on at least one surface in a thickness direction
of the precursor layer by applying a second silicone resin composition
which contains a third organopolysiloxane, a fourth organopolysiloxane, a
hydrosilylation catalyst, and a curing retardant containing
tetraalkylammonium hydroxide.

Claims:

1. A method for producing a silicone resin sheet, comprising the steps
of: forming a first coating layer by applying a first silicone resin
composition which contains a first organopolysiloxane having at least two
alkenylsilyl groups in one molecule and a second organopolysiloxane
having at least two hydrosilyl groups in one molecule; forming a
precursor layer from the first coating layer by reacting the first
organopolysiloxane with the second organopolysiloxane so as to have a
conversion ratio of 5 to 40%; and forming a second layer on at least one
surface in a thickness direction of the precursor layer by applying a
second silicone resin composition which contains a third
organopolysiloxane having at least two alkenylsilyl groups in one
molecule, a fourth organopolysiloxane having at least two hydrosilyl
groups in one molecule, a hydrosilylation catalyst, and a curing
retardant containing tetraalkylammonium hydroxide.

2. The method for producing a silicone resin sheet according to claim 1,
wherein in the step of forming the precursor layer, the first
organopolysiloxane is reacted with the second organopolysiloxane by
heating the first coating layer.

3. The method for producing a silicone resin sheet according to claim 1,
wherein in the step of forming the precursor layer, the first
organopolysiloxane is reacted with the second organopolysiloxane by
heating the first coating layer at 80 to 110.degree. C. for 3 to 8
minutes.

4. The method for producing a silicone resin sheet according to claim 1,
further comprising the step of semi-curing the second layer.

5. The method for producing a silicone resin sheet according to claim 1,
wherein the alkenylsilyl group is a vinylsilyl group.

6. The method for producing a silicone resin sheet according to claim 1,
wherein the first silicone resin composition or the second silicone resin
composition contains a functionality-imparting agent.

7. The method for producing a silicone resin sheet according to claim 1,
wherein the first silicone resin composition contains a first
functionality-imparting agent and the second silicone resin composition
contains a second functionality-imparting agent which has a different
function from that of the first functionality-imparting agent.

8. A silicone resin sheet comprising: a first layer formed by reacting a
first silicone resin composition which contains a first
organopolysiloxane having at least two alkenylsilyl groups in one
molecule and a second organopolysiloxane having at least two hydrosilyl
groups in one molecule so as to have a conversion ratio of 5 to 40% and a
second layer laminated on at least one surface in a thickness direction
of the first layer and formed from a second silicone resin composition
which contains a third organopolysiloxane having at least two
alkenylsilyl groups in one molecule, a fourth organopolysiloxane having
at least two hydrosilyl groups in one molecule, a hydrosilylation
catalyst, and a curing retardant containing tetralkylammonium hydroxide.

9. The silicone resin sheet according claim 8, wherein the second layer
is in a semi-cured state.

10. An encapsulating sheet made of a silicone resin sheet, wherein the
silicone resin sheet comprises: a first layer formed by reacting a first
silicone resin composition which contains a first organopolysiloxane
having at least two alkenylsilyl groups in one molecule and a second
organopolysiloxane having at least two hydrosilyl groups in one molecule
so as to have a conversion ratio of 5 to 40% and a second layer laminated
on at least one surface in a thickness direction of the first layer and
formed from a second silicone resin composition which contains a third
organopolysiloxane having at least two alkenylsilyl groups in one
molecule, a fourth organopolysiloxane having at least two hydrosilyl
groups in one molecule, a hydrosilylation catalyst, and a curing
retardant containing tetralkylammonium hydroxide.

11. A light emitting diode device comprising: a board, a light emitting
diode element mounted on the board, and an encapsulating sheet formed on
one surface in a thickness direction of the board so as to encapsulate
the light emitting diode element, wherein the encapsulating sheet is made
of a silicone resin sheet, and the silicone resin sheet comprises: a
first layer formed by reacting a first silicone resin composition which
contains a first organopolysiloxane having at least two alkenylsilyl
groups in one molecule and a second organopolysiloxane having at least
two hydrosilyl groups in one molecule so as to have a conversion ratio of
5 to 40% and a second layer laminated on at least one surface in a
thickness direction of the first layer and formed from a second silicone
resin composition which contains a third organopolysiloxane having at
least two alkenylsilyl groups in one molecule, a fourth
organopolysiloxane having at least two hydrosilyl groups in one molecule,
a hydrosilylation catalyst, and a curing retardant containing
tetralkylammonium hydroxide.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority from Japanese Patent
Application No. 2011-206291 filed on Sep. 21, 2011, the contents of which
are hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a silicone resin sheet, a
producing method thereof, an encapsulating sheet, and a light emitting
diode device, to be specific, to a method for producing a silicone resin
sheet, a silicone resin sheet obtained by the method, an encapsulating
sheet made of the silicone resin sheet, and a light emitting diode device
in which a light emitting diode element is encapsulated by the
encapsulating sheet.

[0004] 2. Description of Related Art

[0005] It has been known that a silicone resin sheet formed from a
silicone resin (a silicone elastomer material) having an excellent light
resistance and heat resistance into a sheet shape is used in various
uses.

[0006] For example, a method in which after applying a mixture of an
addition reaction curable type silicone gel material mainly composed of
an organopolysiloxane and an addition reaction curable type silicone
rubber material mainly composed of an organopolysiloxane onto a substrate
in a sheet shape, the mixture is cured by heating at 150° C. for 5
minutes, so that a silicone gel sheet is produced has been proposed (ref:
for example, Japanese Unexamined Patent Publication No. 2008-291232).

SUMMARY OF THE INVENTION

[0007] However, there may be a case where a silicone resin sheet is
required to be formed of a plurality of layers having different functions
in accordance with its use and purpose. In such a case, a method in which
the mixture in Japanese Unexamined Patent Publication No. 2008-291232 is
applied to the upper surface of a lower side silicone resin layer formed
in a sheet shape in advance to be then cured by heating, so that an upper
side silicone resin layer is formed has been tentatively proposed.

[0008] However, in the silicone resin sheet obtained by the tentative
proposal, there is a disadvantage that a peeling easily occurs at the
interfacial surface between the upper side silicone resin layer and the
lower side silicone resin layer.

[0009] It is an object of the present invention to provide a silicone
resin sheet in which an interfacial peeling between a first layer and a
second layer is effectively suppressed, a producing method thereof, an
encapsulating sheet made of the silicone resin sheet, and a light
emitting diode device in which a light emitting diode element is
encapsulated by the encapsulating sheet.

[0010] A method for producing a silicone resin sheet of the present
invention includes the steps of forming a first coating layer by applying
a first silicone resin composition which contains a first
organopolysiloxane having at least two alkenylsilyl groups in one
molecule and a second organopolysiloxane having at least two hydrosilyl
groups in one molecule; forming a precursor layer from the first coating
layer by reacting the first organopolysiloxane with the second
organopolysiloxane so as to have a conversion ratio of 5 to 40%; and
forming a second layer on at least one surface in a thickness direction
of the precursor layer by applying a second silicone resin composition
which contains a third organopolysiloxane having at least two
alkenylsilyl groups in one molecule, a fourth organopolysiloxane having
at least two hydrosilyl groups in one molecule, a hydrosilylation
catalyst, and a curing retardant containing tetraalkylammonium hydroxide.

[0011] In the method for producing a silicone resin sheet of the present
invention, it is preferable that in the step of forming the precursor
layer, the first organopolysiloxane is reacted with the second
organopolysiloxane by heating the first coating layer.

[0012] In the method for producing a silicone resin sheet of the present
invention, it is preferable that in the step of forming the precursor
layer, the first organopolysiloxane is reacted with the second
organopolysiloxane by heating the first coating layer at 80 to
110° C. for 3 to 8 minutes.

[0013] In the method for producing a silicone resin sheet of the present
invention, it is preferable that the step of semi-curing the second layer
is further included.

[0014] In the method for producing a silicone resin sheet of the present
invention, it is preferable that the alkenylsilyl group is a vinylsilyl
group.

[0015] In the method for producing a silicone resin sheet of the present
invention, it is preferable that the first silicone resin composition or
the second silicone resin composition contains a functionality-imparting
agent.

[0016] In the method for producing a silicone resin sheet of the present
invention, it is preferable that the first silicone resin composition
contains a first functionality-imparting agent and the second silicone
resin composition contains a second functionality-imparting agent which
has a different function from that of the first functionality-imparting
agent.

[0017] A silicone resin sheet of the present invention includes a first
layer formed by reacting a first silicone resin composition which
contains a first organopolysiloxane having at least two alkenylsilyl
groups in one molecule and a second organopolysiloxane having at least
two hydrosilyl groups in one molecule so as to have a conversion ratio of
5 to 40% and a second layer laminated on at least one surface in a
thickness direction of the first layer and formed from a second silicone
resin composition which contains a third organopolysiloxane having at
least two alkenylsilyl groups in one molecule, a fourth
organopolysiloxane having at least two hydrosilyl groups in one molecule,
a hydrosilylation catalyst, and a curing retardant containing
tetralkylammonium hydroxide.

[0018] In the silicone resin sheet of the present invention, it is
preferable that the second layer is in a semi-cured state.

[0019] An encapsulating sheet of the present invention is made of the
above-described silicone resin sheet.

[0020] A light emitting diode device of the present invention includes a
board, a light emitting diode element mounted on the board, and the
above-described encapsulating sheet formed on one surface in a thickness
direction of the board so as to encapsulate the light emitting diode
element.

[0021] In the method for producing a silicone resin sheet of the present
invention, the first organopolysiloxane and the second organopolysiloxane
are reacted so as to have a conversion ratio of 5 to 40%, so that the
precursor layer is formed from the first coating layer and the second
silicone resin composition is applied on at least one surface of the
precursor layer to form the second layer. Therefore, on at least one
surface of the precursor layer, the unconverted first organopolysiloxane
and/or second organopolysiloxane, and the third organopolysiloxane and
fourth organopolysiloxane can be reacted with each other.

[0022] Thus, the adhesiveness of the first layer to the second layer in
the silicone resin sheet of the present invention can be improved, so
that the interfacial peeling between the first layer and the second layer
can be effectively suppressed.

[0023] As a result, the long-term reliability of the encapsulating sheet
of the present invention made of the silicone resin sheet of the present
invention and the light emitting diode device in which the light emitting
diode element is encapsulated by the encapsulating sheet of the present
invention can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 shows process drawings for illustrating a first embodiment
of a method for producing a silicone resin sheet of the present
invention:

[0025] (a) illustrating a step of forming a precursor layer and

[0026] (b) illustrating a step of forming a second layer to produce a
silicone resin sheet.

[0027] FIG. 2 shows process drawings for illustrating a method for
encapsulating a light emitting diode element using an encapsulating sheet
made of the silicone resin sheet shown in FIG. 1(b):

[0028] (a) illustrating a step of preparing a board mounted with the light
emitting diode element and

[0029] (b) illustrating a step of encapsulating the light emitting diode
element by the encapsulating sheet.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

[0030] A method for producing a silicone resin sheet includes the steps of
forming a first coating layer by applying a first silicone resin
composition, forming a precursor layer from the first coating layer, and
forming a second layer on the upper surface (one surface in the thickness
direction) of the precursor layer by applying a second silicone resin
composition. In addition, the method for producing a silicone resin sheet
includes the step of semi-curing the second layer.

[0031] The first silicone resin composition is an addition reaction
curable type silicone resin composition and contains a first
organopolysiloxane having an alkenylsilyl group and a second
organopolysiloxane having a hydrosilyl group.

[0032] The first organopolysiloxane is blended in the addition reaction
curable type silicone resin composition as a main agent and in view of
forming a cross-link, has at least two alkenylsilyl groups in one
molecule.

[0033] The alkenylsilyl group is a group in which an alkenyl group is
bonded to a silicon atom and the arrangement of the alkenylsilyl group
may be any of at an end of a molecule, in the main chain, or in a side
chain.

[0034] Examples of the alkenyl group include a substituted or
unsubstituted alkenyl group. The structure of the alkenyl group may be a
straight chain, a branched chain, or cyclic as long as it is an organic
group containing an alkenyl group in a skeleton. The number of carbon
atoms of the organic group is, in view of transparency and heat
resistance, preferably 1 to 20, or more preferably 1 to 10. To be
specific, examples of the alkenyl group include a vinyl group, an allyl
group, a propenyl group, a butenyl group, a pentenyl group, a hexenyl
group, a heptenyl group, an octenyl group, a norbornenyl group, and a
cyclohexenyl group. Of these, in view of reactivity with respect to a
hydrosilylation reaction, preferably, a vinyl group is used.

[0035] That is, as the alkenylsilyl group, pereferably, a vinylsilyl group
(CH2═CH--Si--) is used.

[0036] The organic group bonded to a silicon atom, other than the alkenyl
group, is not particularly limited and an example thereof includes a
monovalent hydrocarbon group.

[0037] Examples of the monovalent hydrocarbon group include a straight
chain, a branched chain, or a cyclic saturated hydrocarbon group or
aromatic hydrocarbon group. The number of carbon atoms of the hydrocarbon
group is, in view of transparency and heat resistance, preferably 1 to
20, or more preferably 1 to 10. To be specific, examples of the
monovalent hydrocarbon group include a methyl group, an ethyl group, a
propyl group, a butyl group, a pentyl group, a hexyl group, a phenyl
group, a naphthyl group, a cyclohexyl group, and a cyclopentyl group. Of
these, in view of transparency, heat resistance, and light resistance of
the obtained resin composition, preferably, a methyl group and a phenyl
group are used, or more preferably, a methyl group is used.

[0038] To be specific, examples of the first organopolysiloxane include a
straight chain structure of vinyl-terminated
polydimethylsiloxane(dimethylvinylsilyl-terminated polydimethylsiloxane),
vinyl-terminated dimethylsiloxane-diphenylsiloxane copolymer,
vinyl-terminated poly(methyl)(phenyl)siloxane, vinyl-terminated
dimethylsiloxane-diethylsiloxane copolymer, trimethylsiloxy-terminated
dimethylsiloxane-methyl(vinyl)siloxane copolymer, vinyl-terminated
dimethylsiloxane-methyl(vinyl)siloxane copolymer, and
trimethylsiloxy-terminated poly(methyl)(vinyl)siloxane. In addition to
the above-described straight chain structure, examples of the molecular
structure of the first organopolysiloxane include a cyclic chain
structure, a branched chain structure, or a three dimensional network
structure. These can be used alone or in combination of two or more.

[0039] A commercially available product can be used as the first
organopolysiloxane. A first organopolysiloxane synthesized in accordance
with a known method can be also used.

[0040] The number average molecular weight (GPC measurement with standard
polystyrene calibration) of the first organopolysiloxane is, for example,
10000 to 100000, or preferably 15000 to 50000.

[0041] The alkenylsilyl functional group equivalent in the first
organopolysiloxane is, in view of toughness and flexibility of the cured
product, preferably 0.005 to 10 mmol/g, or more preferably 0.010 to 5
mmol/g. The functional group equivalent in the first organopolysiloxane
is the number of moles of alkenylsilyl group per 1 g of the first
organopolysiloxane and can be measured by a 1H-NMR using an internal
standard substance. The functional group equivalent in the other
organopolysiloxanes to be described later can be also measured in the
same manner.

[0042] The viscosity of the first organopolysiloxane at 25° C. is,
in view of toughness of the cured product, preferably 100 to 500000 mPas,
or more preferably 300 to 100000 mPas. The viscosity can be measured by
using a B-type viscometer. The viscosity of the other organopolysiloxanes
to be described later can be also measured in the same manner.

[0043] The content of the first organopolysiloxane in the first silicone
resin composition is, for example, 0.1 to 99.9 mass %, or preferably 1 to
99 mass %.

[0044] The second organopolysiloxane is blended in the addition reaction
curable type silicone resin composition as a cross-linking agent and in
view of forming a cross-link, has at least two hydrosilyl groups in one
molecule.

[0045] The hydrosilyl group is a group (--SiH) in which a hydrogen atom is
bonded to a silicon atom and the arrangement of the hydrosilyl group may
be any of at an end of a molecule, in the main chain, or in a side chain.

[0046] The organic group bonded to a silicon atom, other than the
hydrosilyl group, is not particularly limited and an example thereof
includes a monovalent hydrocarbon group.

[0047] An example of the monovalent hydrocarbon group includes the same
monovalent hydrocarbon group as that in the above-described first
organopolysiloxane. Of these, in view of transparency, heat resistance,
and light resistance of the obtained first silicone resin composition,
preferably, a methyl group and a phenyl group are used, or more
preferably, a methyl group is used.

[0048] To be specific, examples of the second organopolysiloxane include a
straight chain structure of dimethylsilyl-terminated
polydimethylsiloxane, dimethylsilyl-terminated
dimethylsiloxane-diphenylsiloxane copolymer, dimethylsilyl-terminated
poly(methyl)(phenyl)siloxane, dimethylsilyl-terminated
dimethylsiloxane-diethylsiloxane copolymer, trimethylsiloxy-terminated
dimethylsiloxane-methyl(hydro)siloxane copolymer
(trimethylsilyl-terminated dimethylsiloxane-methylhydrosiloxane
copolymer), and trimethylsiloxy-terminated poly(methyl)(hydro)siloxane.
In addition to the above-described straight chain structure, examples of
the molecular structure of the second organopolysiloxane include a cyclic
chain structure, a branched chain structure, or a three dimensional
network structure. These can be used alone or in combination of two or
more.

[0049] A commercially available product can be used as the second
organopolysiloxane. A second organopolysiloxane synthesized in accordance
with a known method can be also used.

[0050] The number average molecular weight (GPC measurement with standard
polystyrene calibration) of the second organopolysiloxane is, for
example, 500 to 5000, or preferably 1000 to 3000.

[0051] The hydrosilyl functional group equivalent in the second
organopolysiloxane is, in view of toughness and flexibility of the cured
product, preferably 0.005 to 10 mmol/g, or more preferably 0.010 to 5
mmol/g.

[0052] The viscosity of the second organopolysiloxane at 25° C. is,
in view of toughness of the cured product, preferably 5 to 500000 mPas,
or more preferably 10 to 100000 mPas.

[0053] The content of the second organopolysiloxane in the first silicone
resin composition is preferably 0.1 to 99.9 mass %, or more preferably 1
to 99 mass %.

[0054] The content of the second organopolysiloxane with respect to 100
parts by mass of the first organopolysiloxane is, in view of toughness of
the cured product, preferably 0.1 to 1000 parts by mass, more preferably
1 to 100 parts by mass, even more preferably 1 to 10 parts by mass, or
particularly preferably 1 to 5 parts by mass.

[0055] In the first silicone resin composition, in the molar ratio of the
first organopolysiloxane to the second organopolysiloxane, the molar
ratio (the alkenylsilyl group/the hydrosilyl group) of the
above-described functional groups is preferably 1/50 to 50/1, more
preferably 1/5 to 5/1, or even more preferably 1/2 to 2/1, and
substantially is 1/1.

[0056] The second silicone resin composition is an addition reaction
curable type silicone resin composition and contains a third
organopolysiloxane, a fourth organopolysiloxane, a hydrosilylation
catalyst, and a curing retardant containing tetraalkylammonium hydroxide.

[0057] An example of the third organopolysiloxane includes the examples of
the first organopolysiloxane described above.

[0058] The content of the third organopolysiloxane in the second silicone
resin composition is, for example, 0.1 to 99.9 mass %, or preferably 1 to
99 mass %.

[0059] An example of the fourth organopolysiloxane includes the examples
of the second organopolysiloxane described above.

[0060] The content of the fourth organopolysiloxane in the second silicone
resin composition is, for example, 0.1 to 99.9 mass %, or preferably 1 to
99 mass %.

[0061] The content of the fourth organopolysiloxane with respect to 100
parts by mass of the third organopolysiloxane is, in view of toughness of
the cured product, preferably 0.1 to 1000 parts by mass, more preferably
1 to 100 parts by mass, even more preferably 1 to 10 parts by mass, or
particularly preferably 1 to 5 parts by mass.

[0062] In the second silicone resin composition, in the molar ratio of the
third organopolysiloxane to the fourth organopolysiloxane, the molar
ratio (the alkenylsilyl group/the hydrosilyl group) of the
above-described functional groups is preferably 1/50 to 50/1, more
preferably 1/5 to 5/1, or even more preferably 1/2 to 2/1.

[0063] The hydrosilylation catalyst is not particularly limited as long as
it is a compound which catalyzes a hydrosilylation reaction of the
alkenylsilyl group with the hydrosilyl group. Examples of the
hydrosilylation catalyst include a platinum catalyst such as platinum
black, platinum chloride, chloroplatinic acid, a platinum olefin complex
including a platinum divinyltetramethyldisiloxane complex, a platinum
carbonyl complex, and platinum acetyl acetate; a palladium catalyst; and
a rhodium catalyst. Of these, in view of compatibility, transparency, and
catalyst activity, preferably, a platinum olefin complex is used, or more
preferably, a platinum divinyltetramethyldisiloxane complex is used.

[0064] In the content of the hydrosilylation catalyst, for example, when
the platinum catalyst is used, in view of curing rate, the content of the
platinum with respect to 100 parts by mass of the third
organopolysiloxane is preferably 1.0×10-4 to 0.5 parts by
mass, or more preferably, 1.0×10-3 to 0.05 parts by mass.

[0066] The tetraalkylammonium hydroxide has a suppressing effect on curing
with respect to the hydrosilylation catalyst. The tetraalkylammonium
hydroxide is a hydroxide of ammonium having four alkyl groups (straight
chain, branched chain, or cyclic saturated hydrocarbon groups) which may
have the same or different substituted groups with each other.

[0069] A commercially available product can be used as the
tetraalkylammonium hydroxide. A tetraalkylammonium hydroxide synthesized
in accordance with a known method can be also used.

[0070] As the tetraalkylammonium hydroxide, in view of availability, heat
resistance, and control function of the curing reaction, preferably,
tetramethylammonium hydroxide (TMAH) and tetrabutylammonium hydroxide are
used.

[0071] The tetraalkylammonium hydroxide can be used in any state such as a
solid state, a solution state, or the like. In view of dispersibility
into a silicone resin, preferably, the tetraalkylammonium hydroxide in a
solution state is used.

[0072] In a case where the tetraalkylammonium hydroxide is used as a
solution, the solvent thereof is not particularly limited. An example of
the solvent includes a monohydric alcohol such as methanol and ethanol.

[0073] The content of the tetraalkylammonium hydroxide is, in view of
balance of storage stability and curing properties in a semi-cured state,
preferably 1 to 1000 mol, or more preferably 10 to 500 mol with respect
to 1 mol of the hydrosilylation catalyst.

[0074] The curing retardant can contain, as an optional component, another
curing retardant (a curing retardant excluding the tetraalkylammonium
hydroxide).

[0075] Another curing retardant is not particularly limited as long as it
is a compound which has a suppressing effect on curing with respect to
the hydrosilylation catalyst. Examples thereof include an acetylene
compound, an olefin compound, a phosphorus compound, a nitrogen compound,
a sulfur compound, and an organic peroxide. To be specific, examples
thereof include an acetylene compound such as 1-ethynylcyclohexanol and
3-methyl-1-butyne-3-ol; an olefin compound such as
1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane, and dimethyl
maleate; a phosphorus compound such as triphenylphosphine; a nitrogen
compound such as tributylamine, tetramethylethylenediamine, imidazole,
and benzotriazole; a sulfur compound such as benzothiazole; and an
organic peroxide.

[0076] These other curing retardants can be used alone or in combination
of two or more.

[0077] In a case where another curing retardant is blended, the mixing
proportion is appropriately set according to its purpose and use.

[0078] The first silicone resin composition and the second silicone resin
composition can be respectively prepared by mixing the above-described
components.

[0079] The viscosity of the first silicone resin composition at 25°
C. is adjusted to be, in view of handling ability, for example, 100 to
500000 mPas, or more preferably 300 to 100000 mPas.

[0080] In the second silicone resin composition, for example, a
functionality-imparting agent is contained.

[0081] In the first embodiment, the first silicone resin composition is
prepared only from the first organopolysiloxane and the second
organopolysiloxane without allowing the first silicone resin composition
to contain the functionality-imparting agent.

[0082] The functionality-imparting agent is not particularly limited as
long as it is an agent which is capable of imparting a desired function
to the second silicone resin composition. An example thereof includes an
inorganic particle such as a phosphor, a light reflecting component, and
a filler.

[0083] An example of the phosphor includes a yellow phosphor which is
capable of converting blue light to yellow light (having a wavelength
conversion function). An example thereof includes a phosphor obtained by
doping a metal atom such as cerium (Ce) or europium (Eu) into a composite
metal oxide, a metal sulfide, or the like.

[0084] To be specific, examples of the phosphor include a garnet type
phosphor having a garnet type crystal structure such as
Y3Al5O12:Ce (YAG (yttrium aluminum garnet):Ce), (Y,
Gd)3Al5O12:Ce, Tb3Al3O12:Ce,
Ca3Sc2Si3O12:Ce, and Lu2CaMg2(Si,
Ge)3O12:Ce; a silicate phosphor such as (Sr, Ba)2SiO4
(BOS (barium orthosilicate)):Eu, Ca3SiO4Cl2:Eu,
Sr3SiO5:Eu, Li2SrSiO4:Eu, and
Ca3Si2O7:Eu; an aluminate phosphor such as
CaAl12O19:Mn and SrAl2O4:Eu; a sulfide phosphor such
as ZnS:Cu,Al, CaS:Eu, CaGa2S4:Eu, and SrGa2S4:Eu; an
oxynitride phosphor such as CaSi2O2N2:Eu,
SrSi2O2N2:Eu, BaSi2O2N2:Eu, and
Ca-α-SiAlON; a nitride phosphor such as CaAlSiN3:Eu and
CaSi5N8:Eu; and a fluoride-based phosphor such as
K2SiF6:Mn and K2TiF6:Mn. Preferably, in view of
conversion characteristics of converting blue light to yellow light, a
garnet type phosphor and a silicate phosphor are used, or more
preferably, in view of conversion efficiency, YAG:Ce and BOS:Eu are used.

[0085] These phosphors can be used alone or in combination of two or more.

[0086] The phosphor is in the form of a particle. The shape thereof is not
particularly limited and examples of the shape thereof include a sphere
shape, a flat plate shape, and a needle shape.

[0087] The average value of the maximum length (in the case of a sphere
shape, the average particle size) of the phosphor is, for example, 0.1 to
500 μm, or preferably 0.2 to 200 μm. The average particle size of
the phosphor particle is measured by using a laser diffraction scattering
particle size analyzer.

[0088] The mixing proportion of the phosphor is appropriately adjusted in
accordance with quantum efficiency and scattering properties of the
phosphor and is adjusted so as to have a predetermined color tone such as
white. To be specific, the mixing ratio of the phosphor with respect to
the second silicone resin composition is, for example, 1 to 50 mass %, or
for example, 10 to 40 mass %.

[0089] The light reflecting component is blended so as to improve the
light reflectivity in the second silicone resin composition. An example
of the light reflecting component is a white compound. To be specific, an
example of the white compound includes a white pigment.

[0090] An example of the white pigment includes a white inorganic pigment.
Examples of the white inorganic pigment include an oxide such as titanium
oxide, zinc oxide, and zirconium oxide; a carbonate such as white lead
(lead carbonate) and calcium carbonate; and a clay mineral such as kaolin
(kaolinite).

[0091] As the white inorganic pigment, preferably, the oxide is used, or
more preferably, the titanium oxide is used.

[0092] The titanium oxide can have characteristics such as a high degree
of whiteness, a high light reflectivity, excellent hiding characteristics
(hiding power), excellent coloring characteristics (coloring power), a
high dispersibility, an excellent weather resistance, and a high chemical
stability.

[0093] To be specific, an example of the titanium oxide includes TiO2
(titanium oxide (IV), titanium dioxide).

[0094] The crystal structure of the titanium oxide is not particularly
limited. Examples thereof include a rutile type, a brookite type
(pyromelane), or an anatase type (octahedrite). Preferably, a rutile type
is used.

[0095] The crystal system of the titanium oxide is not particularly
limited. Examples thereof include a tetragonal system or an orthorhombic
system. Preferably, a tetragonal system is used.

[0096] When the crystal structure and the crystal system of the titanium
oxide are the rutile type and the tetragonal system, respectively, it is
possible to effectively prevent a reduction of the reflectivity with
respect to light (to be specific, visible light, among all, the light
around the wavelength of 450 nm) even in a case where a first layer 9 is
exposed to a high temperature for a long time.

[0097] The light reflecting component is in the form of a particle. The
shape thereof is not limited and examples of the shape thereof include a
sphere shape, a plate shape, and a needle shape. The average value of the
maximum length (in the case of a sphere shape, the average particle size)
of the light reflecting component is, for example, 1 to 1000 nm. The
average value of the maximum length is measured by using a laser
diffraction scattering particle size analyzer.

[0098] The mixing ratio of the light reflecting component with respect to
the second silicone resin composition is, for example, 0.5 to 90 mass %,
preferably, in view of coloring characteristics, light reflectivity, and
handling ability of the second silicone resin composition, 1.5 to 70 mass
%.

[0099] The filler is blended as a reinforcing agent as well which imparts
reinforcing properties to the second silicone resin composition. An
example of the filler includes a known filler excluding the
above-described white pigment. To be specific, an example of the filler
includes an inorganic filler and examples of the inorganic filler include
a silica powder, a talc powder, an alumina powder, an aluminum nitride
powder, and a silicon nitride powder.

[0100] As the filler, preferably, in view of reducing linear expansion
coefficient of the second silicone resin composition, a silica powder is
used.

[0101] Examples of the silica powder include a fused silica powder and a
crystalline silica powder. Preferably, a fused silica powder (that is, a
silica glass powder) is used.

[0102] Examples of the shape of the filler include a sphere shape, a plate
shape, and a needle shape. Preferably, in view of excellent filling
properties and fluidity, a sphere shape is used.

[0103] Accordingly, as the silica powder, preferably, a fused silica
powder in a sphere shape is used.

[0104] The average value of the maximum length (in the case of a sphere
shape, the average particle size) of the filler is, for example, 5 to 60
μm, or preferably 15 to 45 μm. The average value of the maximum
length is measured by using a laser diffraction scattering particle size
analyzer.

[0105] The mixing ratio of the filler with respect to the second silicone
resin composition is adjusted to be, for example, 10 to 80 mass %,
preferably 25 to 75 mass %, or more preferably 40 to 60 mass %.

[0107] The viscosity of the second silicone resin composition in which the
functionality-imparting agent is blended at 25° C. is adjusted to
be, in view of handling ability, for example, 100 to 500000 mPas, or more
preferably 300 to 100000 mPas.

[0108] FIG. 1 shows process drawings for illustrating a first embodiment
of a method for producing a silicone resin sheet of the present
invention.

[0109] Next, the method for producing a silicone resin sheet is described
with reference to FIG. 1.

[0110] In this method, first, as shown in FIG. 1(a), the above-described
first silicone resin composition is applied to, for example, the upper
surface of a release film 5.

[0111] Examples of the release film 5 include a resin film made of a resin
such as polyethylene and polyethylene terephthalate (PET) and a metal
foil such as a copper foil and a stainless foil. The release treatment
can be applied to the top surface of the release film 5.

[0112] Examples of an application method of the first silicone resin
composition include a casting, a spin coating, a roll coating, or an
applicator.

[0113] In this way, a first coating layer 2 made of the first silicone
resin composition is formed into a sheet shape.

[0114] The thickness of the first coating layer 2 is, for example, 50 to
500 μm, or preferably 75 to 250 μm.

[0115] Next, a precursor layer 3 is formed from the first coating layer 2.

[0116] To be specific, the first organopolysiloxane and the second
organopolysiloxane are reacted so as to have a conversion ratio of 5 to
40%.

[0117] That is, a hydrosilylation addition reaction of the first
organopolysiloxane with the second organopolysiloxane in the first
coating layer 2 is allowed to proceed partway without being terminated.
That is, the hydrosilylation addition reaction is terminated in the
middle of the reaction.

[0118] To be specific, the first coating layer 2 is heated for a
predetermined duration, so that the first organopolysiloxane and the
second organopolysiloxane are subjected to the hydrosilylation addition
reaction.

[0119] For example, the first coating layer 2 and the release film 5 are
put in, for example, a dryer or the like, so that the first coating layer
2 is heated.

[0120] The heating conditions are appropriately adjusted so that the
conversion ratio is within the above-described range. The heating
temperature (the set temperature of the dryer) is, for example, 70 to
150° C., or preferably, in view of productivity, 80 to 110°
C. The heating duration (the duration of being put in the dryer) is, for
example, 3 to 8 minutes. The heating temperature can be also set to be,
for example, a high temperature which exceeds 150° C. and the
heating duration can be also set to be short hours, for example, less
than 3 minutes, or furthermore not more than 2 minutes.

[0121] After the heating, the hydrosilylation addition reaction is
terminated by, for example, cooling.

[0122] In the first silicone resin composition, when the proportion of the
hydrosilyl group is equimolar or less than equimolar with respect to that
of the alkenylsilyl group, the conversion ratio is calculated as the
ratio (=[(the number of moles of the hydrosilyl group before
reaction)-(the number of moles of the hydrosilyl group after
reaction)]/(the number of moles of the hydrosilyl group before reaction))
of the number of moles of the hydrosilyl group which disappears by the
reaction to the number of moles of the hydrosilyl group before the
reaction.

[0123] The conversion ratio in such a case is calculated from the peak
area of the absorption peak (2150 cm-1) of the Si--H stretching
vibration derived from the hydrosilyl group by measuring the infrared
absorption spectrum. To be specific, the calibration curve is determined
from 0% of the conversion ratio, that is, the peak area of the first
coating layer 2 before the reaction, and 100% of the conversion ratio,
that is, the peak area (that is, 0) after the complete reaction (the
state where the hydrosilyl group does not exist). Then, the conversion
ratio of the first organopolysiloxane is calculated based on the obtained
calibration curve.

[0124] When the conversion ratio exceeds the above-described range, the
number of moles of the unconverted alkenylsilyl group (and/or the
hydrosilyl group) which exists on the top surface of the precursor layer
is excessively small, so that the reaction with the hydrosilyl group
(and/or the alkenylsilyl group) in the second silicone resin composition
to be applied next (described later) becomes insufficient and therefore,
the interlayer adhesiveness between the first layer and the second layer
cannot be sufficiently improved.

[0125] On the other hand, when the conversion ratio is below the
above-described range, it becomes difficult to surely maintain the sheet
shape of the precursor layer or a second layer 4 (described later) made
of the second silicone resin composition to be applied next cannot be
sufficiently supported.

[0126] In this way, as referred in FIG. 1(a), the precursor layer 3 is
formed.

[0127] The thickness of the precursor layer 3 is, for example, 50 to 500
μm or preferably 75 to 250 μm.

[0128] Next, as shown in FIG. 1(b), the second silicone resin composition
is applied to the upper surface (one surface in the thickness direction)
of the precursor layer 3 to form the second layer 4.

[0129] An example of an application method of the second silicone resin
composition includes the same application method as that of the first
silicone resin composition described above.

[0130] The thickness of the second layer 4 is, for example, 400 to 1500
μm, or preferably 500 to 1250 μm.

[0131] Thereafter, the second layer 4 is semi-cured.

[0132] To semi-cure the second layer 4, for example, the second layer 4 is
heated.

[0135] By the heating, a part of (partially) a hydrosilylation reaction of
the third organopolysiloxane with the fourth organopolysiloxane is
progressed, so that the second layer 4 is brought into a semi-cured
(B-stage) state. The second layer 4 is brought into a semi-cured
(B-stage) state, so that, though described in details later, in a case
where a silicone resin sheet 1 is used as an encapsulating sheet 1 (ref:
FIG. 2), even when the second layer 4 comes in contact with a light
emitting diode element 6, the light emitting diode element 6 can be
encapsulated, while the damage thereof can be prevented.

[0136] In this way, the silicone resin sheet 1 including the first layer 9
made of the precursor layer 3 and the second layer 4 formed on the upper
surface thereof can be obtained.

[0137] The thickness of the first layer 9 is, for example, 50 to 500
μm, or preferably 75 to 250 μm and that of the second layer 4 is,
for example, 400 to 1500 μm, or preferably 500 to 1250 μm.

[0138] The silicone resin sheet 1 obtained in this way can be used for
various industrial uses. Among all, the silicone resin sheet 1 obtained
in this way is used as an encapsulating sheet for encapsulating a member
and is preferably used as an encapsulating sheet for encapsulating a
light emitting diode element.

[0139] FIG. 2 shows process drawings for illustrating a method for
encapsulating a light emitting diode element using an encapsulating sheet
made of the silicone resin sheet shown in FIG. 1(b).

[0140] Next, a method for producing a light emitting diode device 8 by
encapsulating the light emitting diode element 6 using the encapsulating
sheet 1 made of the silicone resin sheet 1 is described with reference to
FIG. 2.

[0141] In this method, as shown in FIG. 2(a), a board 7 mounted with the
light emitting diode element 6 is prepared.

[0142] The board 7 is formed into a flat plate shape. On the upper surface
thereof, a terminal (not shown) for being electrically connected to the
light emitting diode element 6 and a wire (not shown) to be continuous
thereto are provided.

[0143] The light emitting diode element 6 is formed on the upper surface
(one side surface in the thickness direction) of the board 7. The light
emitting diode element 6 is mounted on the board 7 by a wire bonding, a
flip-chip bonding, or the like.

[0144] Next, in this method, as shown in FIG. 2(b), the encapsulating
sheet 1 made of the silicone resin sheet 1 is disposed adjacent to the
upper side (one side in the thickness direction) of the board 7.

[0145] To be specific, as shown in phantom lines in FIG. 1(b), the release
film 5 is peeled from the encapsulating sheet 1, then, the encapsulating
sheet 1 shown in FIG. 1(b) is reversed upside down, and as shown by an
arrow in FIG. 2(a), the reversed encapsulating sheet 1 is put on the
board 7 so that the light emitting diode element 6, the terminal, and the
wire are embedded in the second layer 4.

[0146] Thereafter, the encapsulating sheet 1 is heated, so that the second
layer 4 is cured.

[0147] The heating temperature is, for example, 100 to 160° C., or
preferably 120 to 155° C. and the heating duration is, for
example, 10 to 600 minutes, or preferably 60 to 450 minutes.

[0148] In this way, the light emitting diode element 6 is encapsulated by
the second layer 4 in a C-stage (completely cured) state.

[0149] In this way, as shown in FIG. 2(b), the light emitting diode device
8 including the board 7, the light emitting diode element 6, and the
encapsulating sheet 1 can be produced.

[0150] In the above-described method, on the upper surface of the
precursor layer 3, the unconverted first organopolysiloxane and/or second
organopolysiloxane, and the third organopolysiloxane and fourth
organopolysiloxane can be reacted with each other.

[0151] Thus, the adhesiveness of the first layer 9 to the second layer 4
in the silicone resin sheet 1 can be improved, so that the interfacial
peeling between the first layer 9 and the second layer 4 can be
effectively suppressed.

[0152] Among all, the interfacial peeling between the first layer 9 and
the second layer 4 in a C-stage state can be further effectively
suppressed.

[0153] To be specific, the peeling adhesive force (described in details in
next Examples) in a 180-degree peeling test at 25° C. with respect
to the silicone resin sheet 1 in which the second layer 4 is brought into
a C-stage state is, for example, more than 0.5 N/10 mm, preferably not
less than 0.6 N/10 mm, more preferably not less than 0.7 N/10 mm, or
particularly preferably not less than 0.8 N/10 mm, and is, for example,
not more than 10 N/10 mm.

[0154] As a result, the long-term reliability of the encapsulating sheet 1
made of the silicone resin sheet 1 and the light emitting diode device 8
in which the light emitting diode element 6 is encapsulated by the
encapsulating sheet 1 can be improved.

[0155] In addition, the functionality-imparting agent is contained in the
second silicone resin composition, so that the desired function can be
imparted only to the second layer 4. To be specific, the phosphor, the
light reflecting component and/or the filler are contained in the second
silicone resin composition, so that the desired wavelength conversion
function, light reflecting function and/or reinforcing function can be
imparted only to the second layer 4.

Second Embodiment

[0156] In the first embodiment, the functionality-imparting agent is
contained in the second silicone resin composition. Alternatively, for
example, the functionality-imparting agent can be contained in the first
silicone resin composition instead of the second silicone resin
composition.

[0157] For example, the phosphor is contained in the first silicone resin
composition.

[0158] In this way, as referred in FIG. 2(b), the wavelength conversion
function can be imparted to the first layer 9 made of the first silicone
resin composition.

[0159] On the other hand, the functionality-imparting agent is not
contained in the second silicone resin composition. The second silicone
resin composition is prepared only from the third organopolysiloxane, the
fourth organopolysiloxane, the hydrosilylation catalyst, and the curing
retardant. In this way, the second layer 4 is formed.

Third Embodiment

[0160] In the first and second embodiments, the functionality-imparting
agent is contained in either the first silicone resin composition or the
second silicone resin composition. Alternatively, for example, the
functionality-imparting agents (a first functionality-imparting agent and
a second functionality-imparting agent), which have different functions
from each other, can be respectively contained in the first silicone
resin composition and the second silicone resin composition.

[0161] For example, the first functionality-imparting agent can be
contained in the first silicone resin composition and the second
functionality-imparting agent which has a different function from that of
the first functionality-imparting agent can be contained in the second
silicone resin composition.

[0162] To be specific, the phosphor is contained in the first silicone
resin composition and the filler is contained in the second silicone
resin composition.

[0163] In this way, in the light emitting diode device 8, the reinforcing
properties of the second layer 4 can be improved, while the wavelength
conversion function is imparted to the first layer 9.

Other Embodiments

[0164] In the first to third embodiments, the functionality-imparting
agent is contained in at least either the first silicone resin
composition or the second silicone resin composition. Alternatively, for
example, the first silicone resin composition and the second silicone
resin composition can be prepared without imparting the
functionality-imparting agent to neither of them.

[0165] In the first embodiment shown in FIG. 1(b), in the silicone resin
sheet 1, the second layer 4 is formed only on the upper surface (the one
side surface in the thickness direction) of the first layer 9.
Alternatively, for example, though not shown, the second layer 4 can be
also formed on the lower surface (the other side surface in the thickness
direction) of the first layer 9.

EXAMPLES

[0166] While the present invention will be described hereinafter in
further detail with reference to Examples and Comparative Examples, the
present invention is not limited to these Examples and Comparative
Examples.

Example 1

[0167] A first silicone resin composition in which A liquid (a
dimethylvinylsilyl-terminated polydimethylsiloxane, a first
organopolysiloxane) and B liquid (a trimethylsilyl-terminated
dimethylsiloxane-methylhydrosiloxane copolymer, a second
organopolysiloxane) of an addition reaction curable type silicone resin
composition (LR7665, manufactured by WACKER ASAHIKASEI SILICONE CO.,
LTD.) were mixed at a mixing ratio of 1/1 was prepared.

[0168] Next, the first silicone resin composition was applied to the upper
surface of a release film made of PET using an applicator, so that a
first coating layer having a thickness of 100 μm was formed.

[0169] Thereafter, the first coating layer was put in an oven at
90° C. for 5 minutes to be heated, so that A liquid and B liquid
were partially subjected to a hydrosilylation addiction reaction. In this
way, a precursor layer having a thickness of 100 μm was formed.

[0170] Subsequently, the conversion ratio of the hydrosilyl group was
calculated from the peak area of the absorption peak (2150 cm-1) of
the Si--H stretching vibration derived from the hydrosilyl group of the
trimethylsilyl-terminated dimethylsiloxane-methylhydrosiloxane copolymer
of B liquid by measuring the infrared absorption spectrum of the
precursor layer with a FT-IR (manufactured by Thermo Fisher Scientific
K.K.). As a result, the conversion ratio of the hydrosilyl group was 28%.

[0171] Separately, 20 g (1.4 mmol of vinylsilyl group) of a
dimethylvinylsilyl-terminated polydimethylsiloxane (a vinylsilyl group
equivalent of 0.071 mmol/g, a third organopolysiloxane), 0.40 g (1.6 mmol
of hydrosilyl group) of a trimethylsilyl-terminated
dimethylsiloxane-methylhydrosiloxane copolymer (a hydrosilyl group
equivalent of 4.1 mmol/g, a fourth organopolysiloxane), 0.036 mL (1.9
μmol) of a xylene solution (a platinum concentration of 2 mass %) of a
platinum divinyltetramethyldisiloxane complex (a hydrosilylation
catalyst), and 0.063 mL (57 μmol) of a methanol solution (10 mass %)
of tetramethylammonium hydroxide (TMAH, a curing retardant) were mixed to
be stirred at 20° C. for 10 minutes. 50 mass % of a silica (a
filler, an average particle size of 40 μm, manufactured by DENKI
KAGAKU KOGYO KABUSHIKI KAISHA.) was blended into the obtained mixture to
be uniformly stirred and mixed, so that a second silicone resin
composition was prepared.

[0172] Thereafter, the prepared second silicone resin composition was
applied to the upper surface of the precursor layer, so that a second
layer having a thickness of 1000 μm was formed.

[0173] Subsequently, the second layer was put in an oven at 105° C.
for 9 minutes to semi-cure the second silicone resin composition, so that
the second layer in a B-stage state having a thickness of 1000 μm was
formed.

[0174] In this way, a silicone resin sheet including a first layer made of
the precursor layer and the second layer in a B-stage state was produced.

[0175] Thereafter, the silicone resin sheet was put in an oven at
150° C. for 5 hours to completely cure the second layer, so that
the second layer was brought into a C-stage state (a thickness of 1000
μm).

Example 2

[0176] A silicone resin sheet was produced and subsequently, a second
layer was brought into a C-stage state in the same manner as in Example
1, except that the set temperature of the oven in heating the first
coating layer was changed from 90° C. to 105° C.

[0177] The conversion ratio of the hydrosilyl group was 37%.

Comparative Example 1

[0178] A silicone resin sheet was produced and subsequently, a second
layer was brought into a C-stage state in the same manner as in Example
1, except that the set temperature of the oven in heating the first
coating layer was changed from 90° C. to 120° C.

[0179] The conversion ratio of the hydrosilyl group was 42%.

Comparative Example 2

[0180] A silicone resin sheet was produced and subsequently, a second
layer was brought into a C-stage state in the same manner as in Example
1, except that the set temperature of the oven in heating the first
coating layer was changed from 90° C. to 150° C.

[0181] The conversion ratio of the hydrosilyl group was 51%.

[0182] (Evaluation)

[0183] 1. Peeling Test

[0184] (1) 180-degree Peeling Test

[0185] The adhesive force of the first layer to the second layer in a
C-stage state was measured by a 180-degree peeling test.

[0186] To be specific, the silicone resin sheet was cut into a strip shape
having a width of 1 cm to produce a sample. In the sample, a cut was made
between the first layer and the second layer with a cutter to tear one
end portion in the lengthwise direction by 2 cm. Then, the first layer
was fixed to a fixed plate with a universal tensile testing machine and
one end portion in the lengthwise direction of the second layer was held
firmly to be torn off (peeled off) in a direction of 180 degrees with
respect to the first layer.

[0187] The peeling conditions are as follows: under an atmosphere of a
temperature of 23° C. and a humidity of 60% RH, and a peeling rate
of 300 mm/min.

[0188] The results are shown in Table 1.

[0189] (2) The sample after the above-described (1) 180-degree Peeling
Test was observed visually or with an optical microscope, so that a
presence or absence of an interfacial peeling between the first layer and
the second layer was confirmed.

[0190] The results are shown in Table 1.

[0191] In Table 1, the heating conditions and the evaluation are
described.

[0192] While the illustrative embodiments of the present invention are
provided in the above description, such is for illustrative purpose only
and it is not to be construed as limiting the scope of the present
invention. Modification and variation of the present invention that will
be obvious to those skilled in the art is to be covered by the following
claims.